band of noise is even narrower

Bandwidth determined by halfpower points (3-dB down points)

At what point the power drops by 3 dB

Ideal noise band would have infinite drop edges

What is a band of noise described by? How is the relative intensity of the band calculated?

Described by:

the width of the band of frequencies (f2 – f1, in Hz)

the relative intensity of the bandwidth re: one component in the band (in dB)

Relative intensity compared to one component in the bandwidth

Use power formula: 10 log (P1/P2)

P1 - Whole BW in Hz

10 log (bandwidth/1)

Example:

BW = 500 Hz

What is relative intensity of BW?

dB = 10 log 500

log 500 =2.7 dB = 10(2.7) dB = 27

7

What are compnents of noise? How are they related (equation)?

Overall intensity: SPL generated by all components in the noise

Measured by SLM

LPC (level-per-cycle, or spectrum level): SPL generated by one component of the noise

Need to calculate

Bandwidth (in dB or Hz): how wide is the band of noise (in Hz) or the relative level of the band of noise compared to 1 cycle (in dB)

These are related by: OL = LPC + BW (in dB)

8

How do you convert between BW in Hz and BW in dB? How do you calculate LPC?

BW (in dB) = 10 log BW (in Hz)

example: BW (in Hz) = 5500

how wide is BW in dB?

Need to know overall level & BW (in dB or in Hz) and calculate LPC

example: OL = 100 dB SPL

BW (in Hz) = 5500 Hz

what is LPC?

9

Describe the Fletcher and Munson experiment. Who were their subjects? What was their masker? What was their test tone? What was the frequency response of the earphones? What was measured? What was the masked threshold?

Normal subjects

white noise masker (100 dB SPL)

1 kHz test tone

Earphones used were 7000 Hz wide

measured threshold of tone in the white noise masker

masked threshold was 80 dB SPL

what is the critical band?

10

How is the critical band calculated? What is this calculation now called?

Step 1: calculate the LPC of white noise masker

LPC = OL - 10 log BW (in Hz)

LPC = ?

Step 2: calculate width of CB, in dB

BW of CB = OL of CB - LPC of noise

BW of CB = ? (in Hz? in dB?)

This calculation method is now called the Critical Ratio

Calculate the critical band with the values from the Fletcher Munson experiment

OL = 100 dB SPL

BW of earphones = 7000 Hz

OL of CB = 80 dB SPL because rule #2 says power in critical band s threshold for tone

11

How is the critical band measured directly? What ar the findings? What is the width of the NBN masker in audiometers based on?